Loans - Summary Aging of Recorded Investment in Past Due Loans (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Non-PCD Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total	$ 11,871,955	$ 11,843,956
Total Past Due	61,929	59,003
Loans Not Past Due	11,764,721	11,748,037
Nonaccrual Loans	45,305	36,916
Non-PCD Loans [Member] | 30 - 59 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	50,843	33,085
Non-PCD Loans [Member] | 60 - 89 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	10,551	24,226
Non-PCD Loans [Member] | Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total	2,537,240	2,512,544
Total Past Due	18,465	13,529
Loans Not Past Due	2,506,312	2,485,560
Nonaccrual Loans	12,463	13,455
Non-PCD Loans [Member] | Residential Real Estate [Member] | 30 - 59 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	17,555	7,601
Non-PCD Loans [Member] | Residential Real Estate [Member] | 60 - 89 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	910	5,928
Non-PCD Loans [Member] | Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total	6,391,975	6,325,108
Total Past Due	17,949	10,131
Loans Not Past Due	6,353,376	6,302,836
Nonaccrual Loans	20,650	12,141
Non-PCD Loans [Member] | Commercial Real Estate [Member] | 30 - 59 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	10,802	7,554
Non-PCD Loans [Member] | Commercial Real Estate [Member] | 60 - 89 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	7,147	2,577
Non-PCD Loans [Member] | Land Development [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total	929,014	999,923
Total Past Due	4,831	3,692
Loans Not Past Due	921,606	993,715
Nonaccrual Loans	2,577	2,516
Non-PCD Loans [Member] | Land Development [Member] | 30 - 59 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	4,757	1,343
Non-PCD Loans [Member] | Land Development [Member] | 60 - 89 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	74	2,349
Non-PCD Loans [Member] | Commercial Industrial and Factored Receivables [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total	1,778,526	1,759,074
Total Past Due	18,437	29,081
Loans Not Past Due	1,751,507	1,722,109
Nonaccrual Loans	8,582	7,884
Non-PCD Loans [Member] | Commercial Industrial and Factored Receivables [Member] | 30 - 59 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	15,859	14,924
Non-PCD Loans [Member] | Commercial Industrial and Factored Receivables [Member] | 60 - 89 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	2,043	12,465
Non-PCD Loans [Member] | Consumer and Other [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total	235,200	247,307
Total Past Due	2,247	2,570
Loans Not Past Due	231,920	243,817
Nonaccrual Loans	1,033	920
Non-PCD Loans [Member] | Consumer and Other [Member] | 30 - 59 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,870	1,663
Non-PCD Loans [Member] | Consumer and Other [Member] | 60 - 89 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	377	$ 907
PCD Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total	150,322
Total Past Due	2,919
Loans Not Past Due	113,510
Nonaccrual Loans	33,893
PCD Loans [Member] | 30 - 59 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	2,716
PCD Loans [Member] | 60 - 89 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	203
PCD Loans [Member] | Residential Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total	42,779
Total Past Due	782
Loans Not Past Due	33,150
Nonaccrual Loans	8,847
PCD Loans [Member] | Residential Real Estate [Member] | 30 - 59 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	782
PCD Loans [Member] | Commercial Real Estate [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total	92,281
Total Past Due	870
Loans Not Past Due	71,080
Nonaccrual Loans	20,331
PCD Loans [Member] | Commercial Real Estate [Member] | 30 - 59 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	870
PCD Loans [Member] | Land Development [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total	5,447
Total Past Due	47
Loans Not Past Due	4,066
Nonaccrual Loans	1,334
PCD Loans [Member] | Land Development [Member] | 30 - 59 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	12
PCD Loans [Member] | Land Development [Member] | 60 - 89 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	35
PCD Loans [Member] | Commercial Industrial and Factored Receivables [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total	9,756
Total Past Due	1,217
Loans Not Past Due	5,174
Nonaccrual Loans	3,365
PCD Loans [Member] | Commercial Industrial and Factored Receivables [Member] | 30 - 59 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	1,049
PCD Loans [Member] | Commercial Industrial and Factored Receivables [Member] | 60 - 89 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	168
PCD Loans [Member] | Consumer and Other [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total	59
Total Past Due	3
Loans Not Past Due	40
Nonaccrual Loans	16
PCD Loans [Member] | Consumer and Other [Member] | 30 - 59 days past due [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total Past Due	$ 3